Method and apparatus for monitoring a vehicle brake

ABSTRACT

A braking system for a vehicle includes devices that are configured to apply braking force to a wheel in response to a braking command. A first sensor is disposed to monitor a parameter associated with the braking force, and a spatial sensor is disposed to determine a linear range between the vehicle and a predefined locus point. A controller is operatively connected to the braking system and in communication with the first sensor and the spatial sensor. The controller detects a braking event and determines a time to stop and an applied braking force during the braking event, which is integrated over the time to stop. The braking system is evaluated based upon the total stopping distance and the integrated applied braking force during the braking event. A fault associated with the braking system is determined based upon the evaluation of the braking system.

INTRODUCTION

Vehicles can include on-board monitoring systems to monitor and identifya need for service and/or maintenance of a system.

SUMMARY

A braking system for a vehicle is described, and includes devices thatare configured to apply braking force to a wheel in response to abraking command. A first sensor is disposed to monitor a parameterassociated with the braking force, and a spatial sensor is disposed todetermine a linear range between the vehicle and a predefined locuspoint. A controller is operatively connected to the braking system andin communication with the first sensor and the spatial sensor. Thecontroller includes an instruction set that is executable to detect abraking event and determine an applied braking force during the brakingevent, which can be integrated over a time to stop. A total stoppingdistance during the braking event is monitored, and the braking systemis evaluated based upon the total stopping distance, the time to stopand the integrated applied braking force during the braking event. Afault associated with the braking system is determined based upon theevaluation of the braking system and communicated via a controller.

An aspect of the disclosure includes determining a state of health (SOH)for the braking system based upon the evaluation of the total stoppingdistance, the time to stop and the integrated applied braking forceduring the braking event, and communicating, via a human-machineinterface device, the SOH for the braking system to a vehicle operatorwhen the SOH is less than a threshold SOH.

Another aspect of the disclosure includes determining a state of health(SOH) for the braking system based upon the evaluation of the totalstopping distance, the time to stop and the integrated applied brakingforce during the braking event and communicating, via a telematicsdevice, the SOH for the braking system to an off-board controller whenthe SOH is less than a threshold SOH.

Another aspect of the disclosure includes determining an adjustment tothe applied braking force during a subsequent braking event based uponthe total stopping distance and the integrated applied braking forceduring the braking event.

Another aspect of the disclosure includes determining an initial vehiclespeed at initiation of the braking event, and evaluating, via thecontroller, the braking system based upon the initial vehicle speed, thetotal stopping distance and the integrated applied braking force duringthe braking event.

Another aspect of the disclosure includes the on-vehicle sensormonitoring the total stopping distance during the braking event beingone of a lidar device, a radar device, a global positioning system or anultrasonic device.

Another aspect of the disclosure includes the sensor monitoring theapplied braking force during the braking event being a pressure sensordisposed to monitor hydraulic braking pressure in a master cylinder ofthe braking system.

Another aspect of the disclosure includes the sensor monitoring theapplied braking force during the braking event being a sensor disposedto monitor displacement of a brake piston of the braking system.

Another aspect of the disclosure includes communicating, via atelematics device, the need to service the braking system to anoff-board controller.

Another aspect of the disclosure includes evaluating the braking systembased upon the total stopping distance, the time to stop and theintegrated applied braking force during the braking event, includingdetermining a mean deceleration rate based upon the total stoppingdistance, and evaluating the braking system based upon a relationbetween the integrated applied braking force and the mean decelerationrate.

The above features and advantages, and other features and advantages, ofthe present teachings are readily apparent from the following detaileddescription of some of the best modes and other embodiments for carryingout the present teachings, as defined in the appended claims, when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 schematically shows a portion of a vehicle including a vehiclebraking system and associated controllers, in accordance with thedisclosure; and

FIG. 2 schematically shows an information flow diagram for a brakingmonitoring routine associated with operation of the vehicle that isdescribed with reference to FIG. 1, in accordance with the disclosure.

It should be understood that the appended drawings are not necessarilyto scale, and present a somewhat simplified representation of variouspreferred features of the present disclosure as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes. Details associated with such features will be determined inpart by the particular intended application and use environment.

DETAILED DESCRIPTION

The components of the disclosed embodiments, as described andillustrated herein, may be arranged and designed in variousconfigurations. Thus, the following detailed description is not intendedto limit the scope of the disclosure, as claimed, but is merelyrepresentative of possible embodiments thereof. In addition, whilenumerous specific details are set forth in the following description inorder to provide a thorough understanding of the embodiments disclosedherein, some embodiments can be practiced without some of these details.Moreover, for the purpose of clarity, technical material that isunderstood in the related art has not been described in detail in orderto avoid unnecessarily obscuring the disclosure. Furthermore, thedisclosure, as illustrated and described herein, may be practiced in theabsence of an element that is not specifically disclosed herein.

Referring to the drawings, wherein like reference numerals correspond tolike or similar components throughout the several Figures, FIG. 1,consistent with embodiments disclosed herein, illustrates a portion of avehicle 10 that includes an braking system 30 disposed to exert brakingforce on a vehicle wheel 20 and an associated braking controller 50 thatis illustrative of the concepts described herein. The vehicle 10 may beequipped with an autonomous controller 60 that implements autonomousvehicle functionalities in one embodiment. The vehicle 10 includes, inone embodiment, a four-wheel passenger vehicle with steerable frontwheels and fixed rear wheels. The vehicle 10 may include, by way ofnon-limiting examples, a passenger vehicle, a light-duty or heavy-dutytruck, a utility vehicle, an agricultural vehicle, anindustrial/warehouse vehicle, or a recreational off-road vehicle.

The vehicle wheel 20 is mounted on an axle portion that includes arotatable disc 22, and a wheel speed sensor 24 that is disposed tomonitor rotational position and speed of the disc 22 and thus the wheel20. The braking system 30 includes, in one embodiment, a brake caliper34, a brake actuator 36 and a master cylinder 32 that work in concert togenerate hydraulic pressure to apply braking force to the disc 22 toeffect wheel braking during a braking event. A pressure sensor 38 isdisposed to monitor the hydraulic pressure and the associated appliedbraking pressure in the master cylinder 32. Braking pressure is onemetric associated with applied braking force that may be captured duringa braking event. Other metrics related to braking force may be employedand fall within the scope of this disclosure. Alternatively or inaddition, other braking system configurations may be disposed to applybraking force to the vehicle wheel 20, such as drum brakeconfigurations. Alternatively, another braking system configuration mayinclude electrically-actuated caliper devices that include anelectrically-activated brake piston and a linear sensor that is disposedto monitor linear displacement, i.e., stroke length of a plunger of thebrake piston. Furthermore, braking force can originate from an electricmachine, such as an electric wheel motor or an electric motor/generatorthat is an element of an electrified drivetrain, wherein the appliedbraking force is a reactive torque from the electric device that is partof a regenerative braking event.

In one embodiment, the vehicle 10 includes an operator brake pedal 40,which is disposed in a passenger compartment of the vehicle 10 andemployed by a vehicle operator to generate a braking command. A pedalposition sensor 42 is disposed to monitor operator input to the brakepedal 40. Alternatively or in addition, the braking controller 50 may beconfigured to generate a braking command that can be communicated to themaster cylinder 32 and/or the brake actuator 36 to autonomously commandactuation of the braking system 30 to effect vehicle braking in responseto sensed conditions. The autonomously commanded braking command can beseparate from or in conjunction with the braking command that isgenerated by the operator.

The vehicle 10 may be equipped with a spatial monitoring system 54 thatis disposed to monitor the spatial environment surrounding the vehicle10. The vehicle 10 may be equipped with a Global Positioning System(GPS) 52 for navigation. The vehicle 10 may be equipped with atelematics device 56 to effect extra-vehicle communication. The vehicle10 may be equipped with a Human-Machine Interface (HMI) device 70 toeffect communication with the vehicle operator. Communication betweenthe various controllers may be accomplished with a communication link75.

The braking system 30 is configured to control vehicle braking, andincludes wheel brake devices, e.g., disc-brake elements, calipers,master cylinders, and a braking actuator, e.g., a pedal. Wheel speedsensors monitor individual wheel speeds, and the braking controller 50can be mechanized to include anti-lock braking control functionality.The braking controller 50 may also coordinate braking effort generatedvia the wheel brakes and regenerative braking effort generated via theelectric motor(s) during a braking event. The braking system 30 furtherincludes numerous other components and subsystems that can transferbraking commands and monitor braking performance, each of which may besubject to wear and deterioration during their service life.

The spatial monitoring system 54 can include a controller and one or aplurality of spatial sensors 55, wherein each of the spatial sensors 55is disposed on-vehicle to monitor a field of view of objects andgeographic regions that are proximal to the vehicle 10. The spatialmonitoring system 54 generates digital representations of each of thefields of view including proximate remote objects based upon data inputsfrom the spatial sensors. The spatial monitoring system 54 can evaluateinputs from the spatial sensors 55 to determine a linear range, relativespeed, and trajectory of the vehicle 10 in view of each proximate remoteobject. The remote objects can include a predefined locus point, such asan intersection, a cross-walk, a stop sign at an intersection, etc. Thespatial sensors 55 can be located at various locations on the vehicle10, including the front corners, rear corners, rear sides and mid-sides.The spatial sensors 55 can include a front radar sensor and a camera inone embodiment, although the disclosure is not so limited. Placement ofthe aforementioned spatial sensors 55 permits the spatial monitoringsystem 54 to monitor traffic flow including proximate vehicles and otherobjects around the vehicle 10. Data generated by the spatial monitoringsystem 54 may be employed by a lane mark detection processor (not shown)to estimate the roadway. The spatial sensors 55 can further includeobject-locating sensing devices including range sensors, such as FM-CW(Frequency Modulated Continuous Wave) radars, pulse and FSK (FrequencyShift Keying) radars, and lidar (Light Detection and Ranging) devices,and ultrasonic devices which rely upon effects such as Doppler-effectmeasurements to locate forward objects. The possible object-locatingdevices include charged-coupled devices (CCD) or complementary metaloxide semi-conductor (CMOS) video image sensors, and other knowncamera/video image processors which utilize digital photographic methodsto ‘view’ forward objects including one or more vehicle(s). Such sensingsystems are employed for detecting and locating objects in automotiveapplications and are useable with systems including, e.g., adaptivecruise control, autonomous braking, autonomous steering and side-objectdetection.

The spatial monitoring system 54 can be further configured to monitorvehicle position, vehicle dynamic states and the spatial environmentproximal to the vehicle 10. This includes monitoring and characterizingthe spatial environment proximal to the vehicle 10, which is provided tothe autonomous controller 60 to provide a level of driving automation.Data and signal inputs include spatial environment data in the form ofinputs from the spatial sensor(s) 55 and map data in the form of adetailed 3D map of the surrounding environment and position data fromthe GPS 52. Data inputs further include vehicle dynamic data in the formof data collected from in-vehicle sensors such as gyros and wheel speedsensors and information communicated from other vehicles, e.g., V2Vdata, and information communicated from the infrastructure, e.g., V2Xdata. The collected data from the spatial sensor(s) 55 is employed inlocalization, object detection, and classification algorithms toestimate the position of the current road, the current traffic lane, thetypes and position of objects and obstacles, including both static anddynamic obstacles and objects to estimate motion and behavior ofsurrounding moving obstacles on the road and on the traffic lane. Thespatial monitoring system 54 can monitor and estimate vehicle positionand dynamic states, as described herein. The vehicle position statesinclude geographically defined x- and y-states (e.g., latitude andlongitude), and an angular heading. The vehicle dynamic states includeyaw, lateral acceleration and longitudinal acceleration states.

The spatial sensors 55 associated with the vehicle spatial monitoringsystem 54 are preferably positioned within the vehicle 10 in relativelyunobstructed positions to monitor the spatial environment. As employedherein, the spatial environment includes external elements, includingfixed objects such as signs, poles, trees, houses, stores, bridges,etc., and moving or moveable objects such as pedestrians and othervehicles. Each of these spatial sensors 55 provides an estimate ofactual location or condition of an object, wherein said estimateincludes an estimated position and standard deviation. As such, sensorydetection and measurement of object locations and conditions aretypically referred to as ‘estimates.’ It is further appreciated that thecharacteristics of these spatial sensors 55 are complementary, in thatsome are more reliable in estimating certain parameters than others. Thespatial sensors 55 can have different operating ranges and angularcoverages capable of estimating different parameters within theiroperating ranges. For example, radar sensors may be employed to estimaterange, range rate and azimuth location of an object. A camera with avision processor may be employed in estimating a shape and azimuthposition of the object, but is less efficient at estimating the rangeand range rate of an object. Scanning type lidar sensors may be employedin estimating range and azimuth position. Ultrasonic sensors may beemployed in estimating range. Further, it is appreciated that theperformance of each sensor technology is affected by differingenvironmental conditions. Thus, some of the spatial sensors 55 presentparametric variances during operation, although overlapping coverageareas of the sensors create opportunities for sensor data fusion.

The autonomous controller 60 is configured to effect autonomous vehicleoperation. Autonomous vehicle functionality may include an on-vehiclecontrol system that is capable of providing a level of drivingautomation. The terms ‘driver’ and ‘operator’ describe the personresponsible for directing operation of the vehicle 10, whether activelyinvolved in controlling one or more vehicle functions or directingautonomous vehicle operation. Driving automation can include a range ofdynamic driving and vehicle operation. Driving automation can includesome level of automatic control or intervention related to a singlevehicle function, such as steering, acceleration, and/or braking, withthe driver continuously having overall control of the vehicle 10.Driving automation can include some level of automatic control orintervention related to simultaneous control of multiple vehiclefunctions, such as steering, acceleration, and/or braking, with thedriver continuously having overall control of the vehicle 10. Drivingautomation can include simultaneous automatic control of all vehicledriving functions, including steering, acceleration, and braking,wherein the driver cedes control of the vehicle for a period of timeduring a trip. Driving automation can include simultaneous automaticcontrol of vehicle driving functions, including steering, acceleration,and braking, wherein the driver cedes control of the vehicle 10 for anentire trip. Driving automation includes hardware and controllersconfigured to monitor the spatial environment under various drivingmodes to perform various driving tasks during dynamic vehicle operation.Driving automation can include, by way of non-limiting examples, cruisecontrol, adaptive cruise control, lane-change warning, intervention andcontrol, automatic parking, acceleration, braking, and the like. Theautonomous vehicle functions include, by way of non-limiting examples,an adaptive cruise control (ACC) operation, lane guidance and lanekeeping operation, lane change operation, steering assist operation,object avoidance operation, parking assistance operation, vehiclebraking operation, vehicle speed and acceleration operation, vehiclelateral motion operation, e.g., as part of the lane guidance, lanekeeping and lane change operations, etc. As such, the braking commandcan be generated by the autonomous controller 60 independently from anaction by the vehicle operator and in response to an autonomous controlfunction.

Operator controls can be included in the passenger compartment of thevehicle 10 and may include, by way of non-limiting examples, a steeringwheel, an accelerator pedal, the brake pedal 40 and an operator inputdevice that is an element of the HMI device 70. The operator controlsenable a vehicle operator to interact with and direct operation of thevehicle 10 in functioning to provide passenger transportation. Theoperator control devices including the steering wheel, acceleratorpedal, brake pedal 40, transmission range selector and the like may beomitted in some embodiments of the vehicle 10.

The HMI device 70 provides for human/machine interaction, for purposesof directing operation of an infotainment system, the GPS 52, anavigation system and the like, and includes a controller. The HMIdevice 70 monitors operator requests and provides information to theoperator including status of vehicle systems, service and maintenanceinformation. The HMI device 70 communicates with and/or controlsoperation of a plurality of operator interface devices, wherein theoperator interface devices are capable of transmitting a messageassociated with operation of one of the autonomic vehicle controlsystems. The HMI device 70 may also communicate with one or more devicesthat monitor biometric data associated with the vehicle operator,including, e.g., eye gaze location, posture, and head position tracking,among others. The HMI device 70 is depicted as a unitary device for easeof description, but may be configured as a plurality of controllers andassociated sensing devices in an embodiment of the system describedherein. Operator interface devices can include devices that are capableof transmitting a message urging operator action, and can include anelectronic visual display module, e.g., a liquid crystal display (LCD)device, a heads-up display (HUD), an audio feedback device, a wearabledevice and a haptic seat. The operator interface devices that arecapable of urging operator action are preferably controlled by orthrough the HMI device 70. The HUD may project information that isreflected onto an interior side of a windshield of the vehicle, in thefield of view of the operator, including transmitting a confidence levelassociated with operating one of the autonomic vehicle control systems.The HUD may also provide augmented reality information, such as lanelocation, vehicle path, directional and/or navigational information, andthe like.

In one embodiment, the vehicle 10 can be configured to communicate withan extra-vehicle communication network 85 via the telematics device 56,which includes communicating between a controller associated with anintelligent highway system and the vehicle 10. An intelligent highwaysystem can be configured to monitor locations, speeds and trajectoriesof a plurality of vehicles, with such information employed to facilitatecontrol of one or a plurality of similarly-situated vehicles. This caninclude communicating geographic location, forward velocity andacceleration rate of one or more vehicles in relation to the vehicle 10.In one embodiment, the vehicle 10 is configured to communicate with anoff-board controller 80, such as at a remote service center that employsan off-board administrator, via the communication network 85.

The term “controller” and related terms such as control module, module,control, control unit, processor and similar terms refer to one orvarious combinations of Application Specific Integrated Circuit(s)(ASIC), electronic circuit(s), central processing unit(s), e.g.,microprocessor(s) and associated non-transitory memory component(s) inthe form of memory and storage devices (read only, programmable readonly, random access, hard drive, etc.). The non-transitory memorycomponent is capable of storing machine-readable instructions in theform of one or more software or firmware programs or routines,combinational logic circuit(s), input/output circuit(s) and devices,signal conditioning and buffer circuitry and other components that canbe accessed by one or more processors to provide a describedfunctionality. Input/output circuit(s) and devices includeanalog/digital converters and related devices that monitor inputs fromsensors, with such inputs monitored at a preset sampling frequency or inresponse to a triggering event. Software, firmware, programs,instructions, control routines, code, algorithms and similar terms meancontroller-executable instruction sets including calibrations andlook-up tables. Each controller executes control routine(s) to providedesired functions. Routines may be executed at regular intervals, forexample each 100 microseconds during ongoing operation. Alternatively,routines may be executed in response to occurrence of a triggeringevent. The term ‘model’ refers to a processor-based orprocessor-executable code and associated calibration that simulates aphysical existence of a device or a physical process. The terms‘dynamic’ and ‘dynamically’ describe steps or processes that areexecuted in real-time and are characterized by monitoring or otherwisedetermining states of parameters and regularly or periodically updatingthe states of the parameters during execution of a routine or betweeniterations of execution of the routine. The terms “calibration”,“calibrate”, and related terms refer to a result or a process thatcompares an actual or standard measurement associated with a device witha perceived or observed measurement or a commanded position. Acalibration as described herein can be reduced to a storable parametrictable, a plurality of executable equations or another suitable form.

Communication between controllers, and communication betweencontrollers, actuators and/or sensors may be accomplished using thecommunication link 75, which may be a direct-wired point-to-point link,a networked communication bus link, a wireless link or anothercommunication link. Communication includes exchanging data signals,including, for example, exchanging electrical signals via a conductivemedium, electromagnetic signals via air, optical signals via opticalwaveguides, and the like. The data signals may include discrete, analogor digitized analog signals representing inputs from sensors, actuatorcommands, and communication between controllers. The term “signal”refers to a physically discernible indicator that conveys information,and may be a suitable waveform (e.g., electrical, optical, magnetic,mechanical or electromagnetic), such as DC, AC, sinusoidal-wave,triangular-wave, square-wave, vibration, and the like, that is capableof traveling through a medium. A parameter is defined as a measurablequantity that represents a physical property of a device or otherelement that is discernible using one or more sensors and/or a physicalmodel. A parameter can have a discrete value, e.g., either “1” or “0”,or can be infinitely variable in value.

The telematics device 56 includes a wireless telematics communicationsystem capable of extra-vehicle communications, including communicatingwith the communication network 85 having wireless and wiredcommunication capabilities. The telematics device 56 is capable ofextra-vehicle communications that includes short-rangevehicle-to-vehicle (V2V) communication. Alternatively or in addition,the telematics device 56 has a wireless telematics communication systemcapable of short-range wireless communication to a handheld device,e.g., a cell phone, a satellite phone or another telephonic device. Inone embodiment the handheld device is loaded with a software applicationthat includes a wireless protocol to communicate with the telematicsdevice 56, and the handheld device executes the extra-vehiclecommunication, including communicating with the off-board administratorvia the off-board controller 80 via the communication network 85.Alternatively or in addition, the telematics device 56 executes theextra-vehicle communication directly by communicating with the off-boardcontroller via a communication network.

Various components, subsystems and systems may experience differentrates of deterioration and aging over the service life of a vehicle, andmay benefit from being managed and controlled in a way that imparts lessstress under certain conditions to extend their service life and/ormaintain an acceptable vehicle performance level. Elements of brakes,e.g., brake pads, are serviceable parts that undergo wear in-use, andperiodically need to be replaced to maintain braking performance.Proactive and early detection of brake wear and degraded performance canbe provided to a driver and autonomous control routines. In autonomousbrake control systems, the magnitude of applied braking force may bedetermined based upon a relative speed and a relative distance inrelation to a target, which can be an intersection in one embodiment.

FIG. 2 schematically shows an information flow diagram associated with abraking monitoring routine 200, which can be advantageously implementedin a controller of an embodiment of the vehicle 10 that is describedwith reference to FIG. 1. The braking monitoring routine 200 can beexecuted as one or a plurality of control routines. Overall, the brakingmonitoring routine 200 includes detecting occurrence of a braking eventand monitoring applied braking force during the braking event.Monitoring the applied braking force can be achieved via the pressuresensor 38 that is disposed to monitor the hydraulic pressure and theassociated applied braking pressure in the master cylinder 32 during thebraking event, in one embodiment. A total stopping distance and a timeto stop the vehicle 10 during the braking event are also monitored. Thetime to stop is measured from a beginning point, which is when thebraking event is commanded, and an end point, which is when the vehicle10 has achieved a zero speed state. The applied braking pressure isintegrated over the time to stop. The braking system is evaluated basedupon the total stopping distance and the integrated applied brakingforce during the braking event. A need to service the braking system canbe determined based upon the evaluation of the total stopping distanceand the integrated applied braking force during the braking event.Vehicle stopping distance can vary depending on the brake wear. Thebraking monitoring routine 200 compares stopping distance and time tostop values to a calibrated stopping distance and time to stop values inconjunction with comparing the braking force with a calibrated brakingforce, utilizing existing brake hardware and without adding sensors orother devices that are specifically configured to detect brake wear.

Table 1 is provided as a key wherein the numerically labeled blocks andthe corresponding functions are set forth as follows, corresponding tothe braking monitoring routine 200. The teachings may be describedherein in terms of functional and/or logical block components and/orvarious processing steps. It should be realized that such blockcomponents may be composed of hardware, software, and/or firmwarecomponents that have been configured to perform the specified functions.

TABLE 1 BLOCK BLOCK CONTENTS 201 Vehicle calibration 202 Is vehicleoperating? 204 Is vehicle in Drive, and is vehicle speed greater than aminimum threshold? 206 Is braking commanded? 208 Is there a predefinedlocus point associated with a hard stop? 210 Capture information relatedto calibration stopping event, including initial vehicle speed,cumulative braking force (e.g., pressure), stopping distance 212Calibrate on-vehicle map, stopping distance 220 Vehicle operation 222 Isvehicle operating? 224 Detect vehicle location; Is location on map =calibrated map? 226 Detect and monitor stop event (stopping distance,applied braking pressure, distance); Is stop = calibrated stop? 228Compare stopping distance, accumulated braking pressure for distance 230Is difference greater than threshold? 232 Increment event counter 234Frequency of events greater than maximum threshold? 236 Issue notice tooperator 238 Update calibrated time to stop 240 Executediagnosis/prognosis routine 242 Execute fault isolation routine 244Execute SOH monitoring of braking system

The braking monitoring routine 200 includes a vehicle calibrationsubroutine 201 and a vehicle operation subroutine 220. A braking eventis any event during vehicle operation in which vehicle braking iscommanded, either by an operator or by an autonomous control system. Astopping event is a braking event that results in the vehicle 10achieving a stop condition, i.e., reaching zero speed. The designationof (1) indicates that the described condition is TRUE, or achieved, andthe designation of (0) indicates that the described condition is FALSE,or not achieved. The vehicle calibration subroutine 201 includesverifying that the vehicle is operating (202)(1), verifying that thevehicle is operating in a forward gear and that the vehicle speed isgreater than a minimum threshold speed (204)(1), verifying the presenceof a braking command (206)(1), and verifying the presence of apredefined locus point, such as a stop sign, a crosswalk, a traffic lampat an intersection or other related stop event (208)(1). When all theaforementioned conditions are achieved, data associated with thecalibration stopping event is captured in an on-board memory device andformed into a database (210), including an initial vehicle speed,cumulative braking force, e.g., pressure, a time to stop and stoppingdistance. Preferably, the stopping distance is determined employinginformation from the spatial sensors 55 of the spatial monitoring system54, e.g., the lidar sensors that estimate linear range and azimuthposition. Location of the vehicle 10 as indicated by the GPS 52 may alsobe captured, and a target stopping distance can be associated with anon-vehicle map for the GPS location (212). The result from the vehiclecalibration subroutine 201 can be in the form of a lookup table that isstored in a memory array in the controller, and include, for thelocation indicated by the on-vehicle map, a braking force required toachieve a stopping distance and/or a time to stop that is related to aninitial vehicle speed. Such information is captured in an on-vehiclecontroller, or alternatively, in an off-vehicle controller for referenceduring subsequent stopping events. The vehicle calibration subroutine201 described herein is one embodiment of a method for calibrating anembodiment of the vehicle 10 to determine a vehicle-specific empiricalrelationship between vehicle speed, cumulative applied braking force,time to stop, and stopping distance. As described with reference to thevehicle operation subroutine 220, additional vehicle data in the form ofinitial vehicle speeds, cumulative braking forces, e.g., pressure, timesto stop and stopping distances can be captured and incorporated into thedatabase in order to cover braking events over a broad range of brakingsituations, weather conditions and brake temperatures. These additionalelements may also be incorporated into the database, including employingnormalization models that take such factors into account in determiningthe relationship between vehicle speed, cumulative applied brakingforce, time to stop, and stopping distance.

Operation of the vehicle operation subroutine 220 executes as follows.When the vehicle is operating (222)(1), the GPS 52 verifies that thevehicle 10 is operating in a location that has been calibrated (224)(1),and determines whether the vehicle 10 executes a stopping event,including a stopping event having conditions that are related to one ofthe calibrated stopping events of the vehicle calibration subroutine 201(226)(1). This includes capturing data associated with the presentstopping event, including an initial vehicle speed, cumulative brakingpressure, time to stop and stopping distance. The captured dataassociated with the present stopping event is compared with calibrationdata for the stopping event (228), and forwarded to adiagnostic/prognostic routine (240) for evaluation.

The diagnostic/prognostic routine (240) includes a state of health (SOH)monitoring step 242 and a fault isolation step 244. The terms“prognostic”, “prognosis”, and related terms are associated with datamonitoring and algorithms and evaluations that render an advanceindication of a likely future event associated with a component, asubsystem, or a system, such as the braking system 30 of the vehicle 10.Prognostics can include classifications that include a first state thatindicates that the component, subsystem, or system is operating inaccordance with its specification (“Green” or “G”), a second state thatindicates deterioration in the operation of the component, subsystem, orsystem (“Yellow” or “Y”), and a third state that indicates a change or afault in the operation of the component, subsystem, or system (“Red” or“R”) that requires immediate attention by the operator. The terms“diagnostics”, “diagnosis” and related terms are associated with datamonitoring and algorithms and evaluations that render an indication ofpresence or absence of a specific fault with a component, subsystem orsystem. The term “mitigation” and related terms are associated withoperations, actions or control routines that operate to lessen theeffect of a fault in a component, subsystem or system.

The SOH monitoring step 242 includes a determination of the SOH of thebraking system 30, wherein the SOH is determined based upon evaluationand correlation of the data associated with the stopping events,including the initial vehicle speed, cumulative braking pressure, thetime to stop and stopping distance. Green status may be assigned to astopping distance and/or a time to stop that is less than a firstthreshold for an initial vehicle speed, and Yellow status may beassigned to a stopping distance and/or a time to stop that is greaterthan the first threshold for an initial vehicle speed, and less than asecond threshold for the initial vehicle speed. Red status may beassigned to a stopping distance and/or a time to stop that is greaterthan the second threshold for the initial vehicle speed. The brakingmonitoring routine 200 may send a message to the vehicle operator viathe HMI device 70 or an off-board administrator to arrange brake servicewhen the SOH of the braking system 30 is Yellow and the vehicle 10 isconfigured as an autonomous vehicle. The braking monitoring routine 200may be capable of commanding an intervention, such as restrictedoperation or vehicle disablement when the SOH of the braking system 30is Red.

The fault isolation step 244 includes evaluation steps to isolate afault to an element in the braking system 30 based upon the dataassociated with the stopping events, including the initial vehiclespeed, cumulative braking pressure, time to stop and stopping distance.In one embodiment, a fault may be isolated to a worn brake pad when thestopping distance is greater than a first threshold stopping distancethat is associated with an initial vehicle speed. In one embodiment, afault may be isolated to a sticky brake caliper when the stoppingdistance is less than a second threshold stopping distance that isassociated with an initial vehicle speed. Other fault isolation routinescan be developed and implemented to isolate faults in other componentsor subsystems of the braking system 30 with the data associated with thestopping events, including the initial vehicle speed, cumulative brakingpressure, time to stop and stopping distance.

A difference is calculated between the stopping distance for thestopping event and one of the calibrated stopping events of the vehiclecalibration subroutine 201, and an absolute value for the difference iscompared to a threshold (230).

When the absolute value for the difference in the stopping distances isless than the threshold (230)(0), this iteration ends, and the routine200 returns to step 224 to await an indication from the GPS 52 that thevehicle 10 is operating in a location that has been calibrated, and theprocess steps repeat.

When the absolute value for the difference in the stopping distances isgreater than the threshold (230)(1), an event counter is incremented(232), and the event counter is compared to a maximum threshold (234).When the maximum threshold is exceeded (234)(1), the result iscommunicated to the vehicle operator or administrator (236) and a valuefor the calibrated time to stop associated with the stopping event isupdated (238). The updated time to stop for the stopping event isprovided as input to update the data associated with the calibrationstopping event as captured in step 210.

One method for evaluating wear or system degradation of the brakingsystem 30 includes determining a mean deceleration rate based upon thetotal stopping distance and the total time to stop, and evaluating thebraking system 30 based upon a relation between the integrated appliedbraking force and the mean deceleration rate. A decrease in the meandeceleration rate for a known value of the integrated applied brakingforce may indicate increased wear or a decrease in the SOH.

In this manner, monitoring of the initial vehicle speed, cumulativebraking pressure, time to stop and stopping distance, and a comparisonto previously captured data can be employed to monitor brake performanceto detect brake wear. Other factors, e.g., weather and ambientconditions, road surface conditions, etc. may interfere with orotherwise affect results. Furthermore, electric power generation as aresult of regenerative braking may be reviewed to determine themagnitude of braking force, and thus can be monitored. As such, thesystem can advantageously employ historical data to sense a changedegradation in braking performance and then changes the system inputs inresponse to maintain braking performance. When braking performancedegrades below a threshold, the vehicle operator and/or autonomouscontroller 60 is informed that there is a need for maintenance andservice, including a portion of the braking system likely needingservice. The autonomous controller 60 may communicate the SOH of brakingsystem 30 to the off-board administrator via the telematics device 56.

The flowchart and block diagrams in the flow diagrams illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which includes one or more executable instructions forimplementing the specified logical function(s). It will also be notedthat each block of the block diagrams and/or flowchart illustrations,and combinations of blocks in the block diagrams and/or flowchartillustrations, may be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions. These computerprogram instructions may also be stored in a computer-readable mediumthat can direct a controller or other programmable data processingapparatus to function in a particular manner, such that the instructionsstored in the computer-readable medium produce an article of manufactureincluding instructions to implement the function/act specified in theflowchart and/or block diagram block or blocks.

The detailed description and the drawings or figures are supportive anddescriptive of the present teachings, but the scope of the presentteachings is defined solely by the claims. While some of the best modesand other embodiments for carrying out the present teachings have beendescribed in detail, various alternative designs and embodiments existfor practicing the present teachings defined in the appended claims.

What is claimed is:
 1. A method for monitoring a braking system for a vehicle, the method comprising: detecting a braking event; determining an applied braking force during the braking event; integrating the applied braking force during the braking event; monitoring, via a sensor, a total stopping distance during the braking event and a time to stop; evaluating, via a controller, the braking system based upon the total stopping distance, the time to stop and the integrated applied braking force during the braking event; determining a fault associated with the braking system based upon the evaluation of the braking system; and communicating, via the controller, the fault associated with the braking system.
 2. The method of claim 1, further comprising: determining a state of health (SOH) for the braking system based upon the evaluation of the total stopping distance, the time to stop and the integrated applied braking force during the braking event; and communicating, via a human-machine interface device, the SOH for the braking system to a vehicle operator when the SOH is less than a threshold SOH.
 3. The method of claim 1, further comprising: determining a state of health (SOH) for the braking system based upon the evaluation of the total stopping distance, the time to stop and the integrated applied braking force during the braking event; and communicating, via a telematics device, the SOH for the braking system to an off-board controller when the SOH is less than a threshold SOH.
 4. The method of claim 1, further comprising determining an adjustment to the applied braking force during a subsequent braking event based upon the total stopping distance and the integrated applied braking force during the braking event.
 5. The method of claim 1, further comprising: determining an initial vehicle speed at initiation of the braking event; and evaluating, via the controller, the braking system based upon the initial vehicle speed, the total stopping distance and the integrated applied braking force during the braking event.
 6. The method of claim 1, wherein the on-vehicle sensor monitoring the total stopping distance during the braking event comprises a lidar device.
 7. The method of claim 1, wherein determining the applied braking force during the braking event comprises monitoring, via a pressure sensor, hydraulic braking pressure in a master cylinder of the braking system.
 8. The method of claim 1, further comprising communicating, via a telematics device, a need to service the braking system to an off-board controller based upon the fault associated with the braking system.
 9. The method of claim 1, wherein evaluating the braking system based upon the total stopping distance, the time to stop and the integrated applied braking force during the braking event comprises: determining an initial vehicle speed at initiation of the braking event; determining a mean deceleration rate based upon the initial vehicle speed, the total stopping distance and the time to stop; and evaluating the braking system based upon a relation between the integrated applied braking force and the mean deceleration rate.
 10. A vehicle, comprising: a braking system configured to apply a braking force to a wheel in response to a braking command; a first sensor disposed to monitor a parameter associated with the braking force; a spatial monitoring system including a spatial sensor, wherein the spatial sensor is disposed to determine a linear range between the vehicle and a predefined locus point; a first controller, operatively connected to the braking system and in communication with the first sensor and the spatial monitoring system, the first controller including an instruction set, the instruction set executable to: detect a braking command for a braking event, monitor the braking force applied to the wheel during the braking event and a time to stop, determine a total vehicle stopping distance for the braking event; evaluate the braking system based upon the total vehicle stopping distance, the time to stop and the braking force that is applied during the braking event, and determine a need to service the braking system based upon the evaluation of the braking system, including the total vehicle stopping distance, the time to stop and the braking force applied during the braking event.
 11. The vehicle of claim 10, wherein the braking command is generated by a vehicle operator.
 12. The vehicle of claim 10, further comprising: an autonomous controller configured to monitor the braking system and in communication with the first controller, wherein the braking command is generated by the autonomous controller in response to input from the spatial sensor.
 13. The vehicle of claim 10, wherein the spatial sensor comprises one of a lidar sensor, a radar device and an ultrasonic device.
 14. The vehicle of claim 10, wherein the spatial monitoring system includes a global positioning system.
 15. The vehicle of claim 10, wherein the braking system includes a pressure actuation cylinder, wherein the first sensor comprises a pressure sensor is disposed to the pressure actuation cylinder; and wherein the instruction executable to determine the braking force applied during the braking event comprises the instruction set executable to monitor, via the pressure sensor, hydraulic braking pressure in the pressure actuation cylinder of the braking system.
 16. The vehicle of claim 10, wherein the braking system includes a master cylinder, and wherein the first sensor comprises a pressure sensor disposed to monitor hydraulic pressure in the master cylinder; and wherein the instruction executable to determine the braking force applied during the braking event comprises the instruction set executable to monitor, via the pressure sensor, hydraulic braking pressure in the master cylinder of the braking system.
 17. The vehicle of claim 10, wherein the braking system includes an electrically-activated brake piston, wherein the first sensor comprises a sensor disposed to monitor linear displacement of a plunger of the brake piston; and wherein the instruction executable to determine the braking force applied during the braking event comprises the instruction set executable to monitor, via the sensor, the linear displacement of the plunger of the brake piston.
 18. The vehicle of claim 10, further comprising a human-machine interface device in communication with the first controller, wherein the instruction set is executable to: determine a state of health (SOH) for the braking system based upon the evaluation of the total stopping distance, the time to stop and the integrated applied braking force during the braking event; and communicate, via the human-machine interface device, the SOH for the braking system to a vehicle operator when the SOH is less than a threshold SOH.
 19. The vehicle of claim 10, further comprising a telematics device in communication with the first controller; wherein the instruction set is executable to: determine a state of health (SOH) for the braking system based upon the evaluation of the total stopping distance, the time to stop and the integrated applied braking force during the braking event; and communicate, via the telematics device, the SOH for the braking system to an off-board controller when the SOH is less than a threshold SOH. 